This invention relates to the thermal imaging of a scene being observed. More particularly, it concerns the monitoring by infrared means of the thermal energy radiated from a scene by a sensor which can be used passively for day or night imaging.
Present interest in viewing scenes in low light or at night have led to the development and consideration of many schemes for making such scenes visible to the human eye. Some methods are based on the method of utilizing an infrared radiation source to illuminate the scene to be viewed and then receiving the reflected infrared radiation which is transformed into a video sensor for viewing. As an alternative, other methods have developed techniques for passive day or night imaging.
One technique utilizes low light level television cameras. Low light level TV sensors are similar to any standard TV sensor but use an intensified vidicon that makes the sensors exceptionally sensitive to whatever amount of visible light that does exist. A major disadvantage is that the sensor does require some small amount of visible light; it will not operate in total darkness.
Another technique has been perfected through the use of pyroelectric vidicon TV cameras. Pyroelectric vidicon cameras are similar to standard TV cameras except that the target of the vidicon tube is sensitive to the thermal radiation emitted from the scene of interest. The pyroelectric vidicon camera may be utilized either in daylight or night conditions. It has a major disadvantage in that the pyroelectric vidicon camera lacks sensitivity and has poor resolution.
A further method is the forward looking infrared system (FLIR). The FLIR is the most sensitive method to date for detecting and imaging the thermal pattern of a scene of interest. Limitations with this technique are that the scene of interest has to be scanned across the detector and the detector needs to be cooled. These restrictions often cause FLIR reliability and maintainability to be poor. In addition, the expense of the FLIR system is high.
A need clearly exists for the development of a thermal imaging system for passive use in daylight or nighttime conditions, and a system that is capable of providing good resolution and sensitivity at a moderate cost.